There is a critical unmet need in the field of medicine for non-invasive measurement of respiratory parameters in spontaneously breathing patients. Presently, most respiratory medical equipment is used for the long-term monitoring of patients receiving mechanical ventilation. Because most mechanically ventilated patients are intubated, many respiratory parameters can be precisely measured in a way not possible with non-intubated patients. These parameters include those obtained from capnometry, including end tidal CO2 [EtCO2] and CO2 waveform measurements, tidal volume (VT), airway pressure (Paw), minute ventilation (VE), respiratory rate (RR), respiratory effort/work of breathing (RE/WOB), inspiratory:expiratory (I:E) ratio, and dead space measurements.
Thus, while patients in the OR and ICU may receive intensive respiratory monitoring, similarly reliable monitoring is not presently available for non-intubated patients who are often ambulatory, such as those on general care floors and other areas of the hospital. Numerous organizations including the FDA, ASA and APSF have noted this lack of monitoring to be problematic and are calling for new technological advances to migrate intensive respiratory monitoring to non-intubated patients. There is also a critical need for improved monitoring of patients receiving patient controlled anesthesia (PCA) since opioids frequently lead to respiratory depression and subsequent morbidity or mortality. Efforts to identify patients likely to suffer respiratory depression or arrest in a preemptive manner have been only partially successful and adequate monitoring solutions are still lacking even if such patients are identified.
Polysomnography (PSG) is a method of monitoring patients for the evaluation of sleep apnea. PSG uses non-invasive technology but much of it cannot be readily adapted for monitoring patients in the hospital because it is cumbersome and costly. Further, while PSG may be effective in determining if a patient has sleep apnea and further categorizing what type of sleep apnea (central v. obstructive), it is not used for real-time continuous monitoring to detect respiratory events. Polysomnographs must be read by trained technicians or physicians and analysis may be very time consuming and so PSG does not lend itself to continuous non-invasive monitoring of ambulatory patients.